NECO 2002 Biology · Question 39

Use the data to answer this question A class of 40 set out to determine the population of lizards in a bound…

Question

Use the data to answer this question A class of 40 set out to determine the population of lizards in a bound field measuring 200 metres by 100 metres using the capture-recapture method. In their first outing, the students captured a total of 360 lizards all of which were marked with indelible ink and then released back into the field. After a one week interval the students went back into the field and caught a total of 250 lizards out of which 150 bore the indelible ink mark. What is the estimated population of lizards in the field?

A.100
B.300
C.400
D.560
E.600

Answer: E. 600

Explanation written with AI and checked against the answer key

Analyze the question: This is a capture-recapture (Lincoln-Petersen) problem. We estimate the total population from the proportion of marked animals in the second sample.

Concept:

Population estimate = (number marked in first catch × total in second catch) ÷ number of marked in second catch

N = (M × n) / m

Where:

M = number marked and released first = 360
n = total caught second time = 250
m = marked ones recaptured = 150

Solution:

N = (360 × 250) / 150

N = 90,000 / 150

N = 600

Check: The fraction of marked lizards in the second sample is 150/250 = 0.6. If 60% of the field's lizards are marked, and 360 are marked in total, then the population is 360 ÷ 0.6 = 600. ✔

Answer: E (600)

Tip: Remember the formula as "first catch × second catch ÷ recaptured marked." The area of the field (200 m by 100 m) and the number of students (40) are just distractors. Always pick out only the three numbers you need.

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